Method and apparatus for lapping valves



Feb. 1, 1949.

G. F. SCHERER IETBOD AND APPARATUS FOR LAPPING VALVES 3 Sheets-Sheet 1 Filed Feb. 6.- 1945 5 Ex: Wag

mm lg uvmvrox GEORGE F. SGHERER BY a a gi Filed Feb. 6, 1945: 1 3 Sheets-Sheet 2 Feb. 1,-1949.- g, F, SCHERER; 2,460,312

METHOD AND APPARATUS FOR LAPPING VALVES mmnon .GEORGE F. SCHERER FIG. 2 BY wv agfi Feb. 1, 1949. F, S 2,460,312

METHOD AND APPARATUS FOR LAPPING VALVES Filed Feb. 6', 1945 3 Sheets-Sheet 3 56 53 Ill! FIG. 4

Patented Feb. 1, 1949 METHOD AND APPARATUS FOR LAPPING VALVES George F. Scherer, San Francisco, Calif., assignor to Rockwell Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Application February 6, 1945, Serial No. 576,391

14 Claims.

1 This invention relates to an improved method and apparatus for lapping various standard types of commercial valves to assure accurate sealing and seating contact between a movable valve member and its seat under service conditions. More particularly the invention relates to the lapping of plug valve members by rotation or oscillation in their seats under service conditions.

Valves which, prior to final assembly, have been very carefully lapped and adjusted to obtain close fitting contact of a rotatable valve member with the seating surface of the valve body, as for example in a plug valve, will, when installed in the service line, frequently develop substantial leaks or binding of the movable valve member, or both. This has been found to be due to distortions usually produced by one or more of three primary causes, namely, stresses produced in the assembly of the various valve parts, line pressures, and operating temperatures. Such difiiculties are particularly noticeable in connection with the plug type of valve, and applies to lubricated as well as non-lubricated valves, and for this reason I have selected for the purpose of explaining my present invention a lubricated type of plug valve now widely used in the art and disclosed in the patent to Nordstrom No. 2,204,440.

In my Patent No. 2,268,723, January 6, 1942, I have disclosed a hot lapping method to compensate for distortions caused by high temperatures which is a substantial improvement over prior lapping methods. It fails, however, to compensate or provide for line pressure and assembly distortions and when used for very high temperature lapping operations considerable quantities of fumes may be generated from the lapping compounds normally used, creating unpleasant and ineflicient working conditions, and in certain cases the fumes are of such nature as to require the use of gas masks by the workmen. In addition, the lapping compound must be thrown on the hot valve member, resulting in inefiicient and wasteful application of relatively expensive compound. These disadvantages, the present invention overcomes in addition to providing improved lapping operation at high temperatures as well as sub-normal temperatures.

In order that these desirable results may be obtained most einciently and expeditiously by use of my present invention, the assembled valve is subjected to predetermined internal pressure and temperature conditions and abrasive lapping compound is injected under pressure between the opposed surfaces of the movable valve member and its seat as the valve member is moved relative to its seat, so that a substantially uniform abrasive or lapping action by said compound will be obtained on all parts of the seating surfaces of the valve member and body.

The lapping of tank car valves in service and without disassembly, injection of lapping compound is disclosed in Patents Nos. 1,604,944 and 1,604,712 to Nordstrom et al., and the pre-stressing of a valve body by internal pressure is disclosed in the Nordstrom Patent No. 2,117,351. However, in tank car service normal atmospheric temperature and pressure conditions prevail, and the pre-stressing method of Patent No. 2,117,351 is not adapted to lapping during the application of the stresses. The present invention involves original contributions to the art over these patented methods in that the lapping operation is performed with an assembled valve with special fittings and is lapped while under pressures and temperatures simulating operating conditions which generally differ materially from normal atmospheric temperature and pressure conditions for diificult services. Since, according to the present invention, the parts of the valve remain fully assembled during the lapping operation, in lapping lubricated valves of the type shown in Nordstrom Patent No. 2,204,440 for example, for which the invention is particularly useful, advantage can be taken of the lubricant grooves with which the valve is provided to facilitate the injection and uniform distribution of the lapping compound between the seating surfaces of the valve without injuring other moving surfaces of the valves by the abrasive compound.

In the lapping of high temperature valves, one important feature of the invention is to employ a fluid medium for transmitting an internal pressure and temperature to the valve parts of a magnitude which equals or exceeds the maximum pressure and temperature to which the valve will be subjected in service, and which will be neutral to the lapping compound and not deleteriousiy affect its abrasive qualities. While various fluids meeting these requirements might be used, I preferably utilize for this purpose an inert non-combustible gas such as nitrogen or carbon dioxide, so that the lapping operation is carried out in the presence of a neutral or reducing atmosphere, thereby eliminating factors of oxidation and carbonization of the abrasive carrier or vehicle, present in the method of my Patent No. 2,268,723, above predetermined temperatures and which limit my patented method to substantially lower maximum temperatures than can be utilized with much greater convenience and efiiciency by the present invention.

It is also the aim and purpose of my invention to provide a valve lapping method and apparatus as above characterized, in the execution of which different grades or types of abrasive compound may be successively effectively employed without disassembling the valve or releasing or reducing the internal pressure or temperature.

The invention further comprehends a novel method and apparatus for lapping valves which will insure maximum working efficiency with increased useful life of the several valve parts in all types of service.

Finally, my invention provides a, novel method and apparatus for lapping valves under conditions closely corresponding to those which will be encountered in actual service, and which involves the use of very simple and inexpensive apparatus, requiring a minimum of skill in its operation to produce with maximum efllciency an accurately lapped valve possessingthe requisite working characteristics for a particular service.

With the foregoing and other objects in view, the invention comprises the novel method and apparatus for fitting or lapping valves and the several steps thereof as will hereinafter be more fully described and claimed in connection with the accompanying drawings wherein I have illustrated one representative example of apparatus as employed in connection with a typical type of lubricated valve, for the purpose of disclosingmeans for injecting the lapping compound, and

Figure 4 is a horizontal sectional view taken substantially on the lin'e 4--4 of Figure 3.

While it will be clear from the above that the present method is of general application to various well known types of valves, for the purpose of this explanation, I have herein shown a valve of the character disclosed in said Nordstrom Patent No. 2,204,440, having a body or casing it (Figure 2) provided at its opposite ends with the bolting flanges II and the passageway I 2 therethrough for the flow of line fluid. The valve body is also formed with a bore having its axis disposed at right angles to the passageway l2 and forming a frusto-conical valve seat [3. With this seat, the peripheral surface of a frusto-conical valve plug I4 is adapted to have close seatin contact and is formed with a port I! therethrough, adapted in one position of said valve plug to align with the passageway I! for the free flow of the line fluid through said plug.

The seat [3 at its larger end is closed by the cover plate It which is rigidly secured to the valve body by means of the stud bolts l1 and nuts [8. When the valve is in working condition, a plug is centrally threaded in the cover plate I 3 as shown in the said Nordstrom patent and adlustably coacts with a ball centrally positioned in a recess in the large end ofthe valve plug 14 to urge said valve plug to its operative position against the tapered seat II of the valve body. Since, in the lapping of the valve, considerably less thrust pressure of the valve plug against its seat is required, I remove said adjusting screw and in place thereof a bushing I3 is threaded into the central opening of the cover plate ll. This bushing has a reduced threaded outer end portion upon which the internally threaded end of a cylindrical housing 2| for a spring 22 is engaged. The upper end of this spring bears against the'flanged lower end of a pin 23 movable through the bore of the bushin i9 and having a recessed flanged head 23 on its upper end urging the ball 24 into the recess 25 in the valve plug H. The pressure of the spring 22 against the stem 23 is regulated by means of the adjustable screw 26 threaded in the lower end of cylinder 2| and having the plate 21 on its upper end providing a seat for the end of said spring. The upper surface of the cover plate I6 is recessed as at 23 to receive the flange of the ball engaging head 23 and the diaphragm shown at 29, is connected with said head 23 and at its outer edge is held against a shoulder 30 formed on the valve body by means of the clamping ring 3|. 3

The valve body ID at the smaller end of the seat I! is formed with a chamber 32 through which a suitable grade of lubricant is normally fed through the operating stem for the plug I4 to a plurality of longitudinal grooves formed in the surface of the valve plug on each side thereof between the diametrically opposite ends of the stem 39.

port i5. rooves is shown at 33. detailed understanding of the lubricant distributing system, reference may be had to the Nordstrom patent last referred to. For the purpose of this description it will suflice to state that in the open and closed positions of the valve plug I 4 the lower ends of the grooves 33 in the valve plug are connected through the dwarf grooves 34 in the valve body I 0 with an annular groove 35 in the large end of the valve plug which is in registering relation with a similar annulars'roove 33 in the wall of the valve body.

For the purpose of lapping the valve plug to its seat, the plug operating stem shown in the Nordstrom patent is removed and in place thereof a sleeve 31 (Figure 3) is threaded into the threaded bore 38 at the top of the valve body, which communicates at its lower end with the chamber 32. This sleeve serves as a hearing for the lapping valve stem 39 which extends there- One of these lubricant distributing through, the lower end of said stem having an integrally formed lug 40 having opposite flat faces, said lug being received in a central recess 4| of similar shape in the equalizing member 42. The bottom face of this member is grooved to receive an upstanding rib 43 formed on the smaller end of the valve plug l4. Therefore when the stem 39 is rotated, the equalizer operates in the usual -way to impart rotative movement to the valve plug without setting up thrust forces against the valve seat at an angle to the axis of the plug. A suitable bearing washer 44 may be interposed between the upper face of; the lug 40 and the lower end of the sleeve 31, the bearing contact being maintained by means of the nut 45 and lock nut 43 threaded upon the upper end or the This sleeve is locked in position by means of the nut 41 threaded on the upper end thereof. Preferably, in order to prevent undue wear of the sleeve 31 and the lug 40 during the lapping operation, these parts are faced with a For a further and more.

suitable wear resisting material such as Stellite.

During, or prior to the lapping operation, a suitable viscous lubricant is injected through the opening 48 in the top extension of the valve body which is the same as the opening shown in the Nordstrom patent for the injection of plastic packing material for the plug operating stem into the annular chamber indicated at 49. This lubricant, in addition to sealing the threads of the sleeve 31, also lubricates the lapping stem 39 by passing through the radial openings 50 connecting the chamber 49 with an internal annular chamber in the sleeve 31 and longitudinally from said chamber 5| into the grooves 52 in the inner wall of said sleeve.

The lapping stem 39 has a longitudinal bore 53 provided with a thread 54 at its upper end receiving one end of a nipple 55. A suitable injecting fitting 56 is connected with the other end of said nipple and by adjustment relative thereto, the lapping compound is injected under pressure downwardly through the bore 53 and through chamber 32 into the distributing grooves 33 of the valve plug I4 by means of which it is uniformly distributed over the peripheral surfaces of the valve seat l3 and the plug H.

In preparing the valve for the lapping operation, the above described parts thereof are fully assembled, the cover plate I6 being securely tightened, by adjustment of the nuts Hi, to its final position with respect to the valve body. In this operation, the same distorting stresses and distortions resulting therefrom will be set up in the body of the valve, as when the valve operating stem and the threaded valve adjusting plug are ultimately assembled with said plug as in the Nordstrom patent.

Referring now to Figure 1 of the drawing, the

plug valve assembl as above described is posiwith. A similar outlet valve 64 for gases of the desired temperature, either above or below normal room temperature, is also connected between the conduit sections 58 and 62. For high temperature lapping, preferably, each of these conduit sections is internally lined with a suitable refractory material indicated at 65. One end of the pipe 66 is connected with the conduit section 51 and to the other end of this pipe a cylinder or reservoir 61 containing a high pressure fluid may be suitably connected for high pressure lapping. A valve 58 is provided for the manual control of the supply of pressure fluid from said cylinder through the pipe 66 to the conduit section 51. If desired for lapping under sub-atmospheric conditions, 61 may be a suction pump. For low temperature lappin suitably chilled gases may be supplied through connection 66.

The apparatus with the assembled valve as above described is employed for the purpose of lapping the valve plug to its seat at either normal or abnormal temperatures and pressures. When used for high or low temperature lapping the apparatus, excepting the accessories, is substantially completely encased within a sectional jacket 69 of a suitable insulating material. The

jacket sections are of course suitably formed for direct surface contact with all parts of the apparatus, and conventional means is provided (not shown) for detachably connecting the several sections of the insulating jacket and clamping the same in fixed relation to said parts of the apparatus. Also, in lapping the valve at elevated temperatures, I provide a blow torch or other suitable source of extraneous heat indicated at 10. This heat source is closely adjacent to the open end of the conduit section 6| so that the flames will be projected therethrough past the valve 63 toheat the pressure fluid admitted to conduit section 51 through pipe 66. It will of course also be understood that the apparatus is equipped with suitable thermometers and pressure gauges so that an accurate indication of the pressure and temperature to which the valve parts are subjected will be available at all times during the lapping of the valve.

For the purpose of rotating or oscillating the valve plug l4 during the lapping operation, a suitable handle or wrench indicated at H is provided and applied to the nuts and 46 on the upper end of the lapping stem 39, or oscillation may be obtained by suitable automatically operating mechanism.

The abrasive compound to be used during the lapping operation preferably consists of a vehicle mixture of a high boiling point mineral oil or other substance which will withstand the elevated or subnormal lapping temperatures without decomposing or greatly changing in physical characteristics, and a fine grade of Carborundum, Alundum or other abrasive powder. The particular type of abrasive is carefully selected in regard to the particular metal or alloy of which the valve is made and the pressure and temperature at which the lapping operation is carried out.

In the lapping of a valve intended for high pressure service at normal temperature, the valves 63 and 64 are closed. High pressure fluid is then admitted from the cylinder 61 to the conduit 65.-

It is to be understood that the valve plug [4 is initially set in its full open position. As the internal fluid pressure buids up until all parts of the valve are subjected to a pressure somewhat in excess of the ratedworking pressure of the valve, the lapping compound is simultaneously injected, in the manner above described, under a pressure sufliciently high to oppose the counteracting internal pressure until all of the longitudinal grooves 33 of the valve plug M are completely filled with the lapping compound. The admission of pressure fluid from the cylinder 61 is then discontinued and the valve plug I4 is rotated or oscillated by means of handle H upon the seating surface I3 of the valve body. This operation is continued for a time depending upon the size of the valve and other factors and may require up to twenty or thirty minutes or more. The film of abrasive compound interposed between the seating surfaces of the valve plug and body during this operation acts thereon to eliminate all unevenness due to distortions of said surfaces caused in the assembly of the valve parts or by the application of the high internal fluid pressure thereto, resulting in smoothly finished, truly circular, tapered seating surfaces on the plug and valve body having closely fitting contact at all points under operating conditions. In the rotation or oscillation of the valve plug, the'high injection pressure upon the lapping compound may be maintained to continuously feed in lapping compound that may be lost from the grooves and surfaces during operation. Thus said compound will be uniformly distributed from the grooves 33 in the valve plug over the surfaces of said plug and the valve body so that all parts of said surfaces will be subjected to substantially the same abrasive action during the lapping operation. When the valve, lapped in the manner above described, is installed in the pressure service line and subjected to the rated working pressure, it will be evident that the seating surfaces of the valve plug and body will be unaffected by such high working pressure and will remain in a truly circular form for close seating and sealing contact with each other when the valve is closed, while also permitting of the unrestricted rotation of the valve plug to its open and closed positions.

In lapping the valve when intended for use in high pressure lines transmitting fluid at relatively high temperatures, the fluid medium for internally stressing the valve parts is preferably an inert non-combustible gas, such as nitrogen or carbon dioxide, which must be neutral to the vehicle used in the lapping compound so that it will not cause combustion or vaporization thereof. Before the gas under pressure is admitted from thelcylinder 81 to the conduit section 51 of the apparatus, the flames from the blow torch III, or other extraneous heat source used, are passed through the conduit section 8i and past the valve II to bring the valve to the proper operating temperature so that when filled with the gas under pressure, it will be at the lapping temperature.

The valves 63 and 64 are then closed and gas is admitted under pressure through conduit section I. When the pressure and temperature of the gas within the valve reach a predetermined degree in excess of the rated maximum working pressure and temperature, the valve 63 is closed and the gas supply shut ofl. Thus the various parts of the valve, in addition to being subjected to substantially the same internal fluid pressure as that which will occur in the actual service of the valve, are also further deformed or distorted by reason of the high temperature of said pressure fluid which substantially equals or exceeds the temperature of the fluid to be transmitted through the line in which the valve is to be installed. The lapping operation with the high pressure injection of the lapping compound is then carried out in the presence of such high internal fluid pressure and temperature on the valve parts, in the manner above explained in connection with the lapping of the valve at normal temperature.

In similar manner, for low temperature lapping at abnormal pressures the apparatus and valve to be lapped are cooled a predetermined amount below the operating temperature before the internal lapping pressure is established in the valve.

During lapping at abnormal temperatures the temperature gradient is fixed by the fluid in the valve approximately the same as when the valve is in service, a. desirable condition which cannot be attained by heating or chilling the valve being lapped from the exterior.

Because of the high internal pressures used during lapping, the vaporizing or boiling point of the abrasive vehicle is raised so that lapping may be carried out effectively at temperatures considerably higher than those heretofore available. Since the major parts of the valve are also in their normal assembled relationship, the lapping operation therefore takes place in the presence of the mechanical distortions which may be set up in assembly. Thus, by means of the present method there is obtained a perfectly lapped, abnormal temperature and pressure valves providing a fiuidtight non-leaking seal between the seating surfaces when the valve is closed and in which sticking 0r jamming of the movable valve member incident to high working pressure or temperature is eliminated.

After lapping is completed the special fittings are removed and replaced by the final valve parts, thus avoiding wear on the final valve stem, ball. ball seat and like parts for which the special fixtures are substituted during lapping.

It is, of course, apparent that when the valve parts are lapped at a high temperature, they will assume a slightly retracted form when cold, and when lapped at low temperatures will assume a slightly expanded form when warm. However, it is found that, in lubricated valves, this is not detrimental, as the lubricant employed has sufficient viscosity at low temperature to provide an adequate seal and good operational characteristics between the seating surfaces of the valve plug and body. When the valve is subjected to the high temperature of the line fluid, the viscosity of the lubricant will be reduced and, since the parts of the valve will also return to the truly aligned form resulting from the lappin operation, a closer contact or fit of the valve plug on its seat will occur so that the thinner lubricant film becomes effective. It will therefore be understood that in valves intended for highrtemperature service, accurate lapping of the movable valve member on its seat is quite essential since at such temperatures the lubricants employed tend to lose their viscosity and sealing properties and an exceedingly close flt of the plug to its seat is required. On the other hand, in a valve intended for use at low temperatures, a relatively loose fit of the valve to its seat is permissible, since it is not difficult to provide a suitable lubricant at such temperatures having the prop er viscosity to seal the valve and prevent leakage.

An important feature of my invention resides in the step of injecting the lapping compound under pressure in opposition to the opposing internal fluid pressure. Thus, in the hot lapping operation, although the high temperature tends to thin out or reduce the viscosity of the abrasive carrier or vehicle, the lappin compound in contact with the seating surfaces of the valve is nevertheless maintained at a substantially constant consistency so that uniform abrasive action of said compound upon the seating surfaces will be obtained throughout the lapping operation. A further advantage of this injection method is that different grades of lapping compound may be successively and efliciently introduced between the seating surfaces of the valve, without dismantling the valve and cleaning the parts. There will thus be obtained superior lapped surfaces which could not be produced by the use of a single grade of lapping compound or abrasive. It is also to be noted that the change from one grade to another of lapping compound does not require the removal of the valve member from its seat, which would permit temperature changes, and, to a certain extent, defeat the purpose of hot lapping the valve.

From the above description it is believed that my new method and the several practical advantages thereof will be clearly understood. It will be appreciated that such a method may be very expeditiously and accurately carried out to lap or fit various types of valves and other structures containing relatively movable parts which are affected in service by temperature, pressure, bolting stresses and the hke, prior to service installation so that under the known predetermined working conditions they will operate satisfactorily at all times and give superior service. For the purpose of practicing my new method I have herein disclosed one simple and inexpensive embodiment of apparatus. However, it will be evident that the valve or other mechanism to be lapped may be mounted or supported during the lapping operation and subjected to the required internal pressure and temperature by means of apparatus of other structural form than that above particularly described. While I have found it most convenient to describe my new method in connection with one particular type of lubricated valve, it is quite evident that the several novel features of my invention may also be employed in the lapping of various other standard valves of the lubricated or non-lubricated type, pumps. engines and the like under service conditions, which ordinary machining methods caried out at atmospheric pressures and temperatures under non-assembled non-service conditions or unot accomplish.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. The method of lapping the seating surfaces of valves which comprises lapping the movable valve member in its seat in the presence of a lapping compound and a uniformly distributed fiuid pressure within the valve body which is at least equal to the rated maximum working pressure of the valve.

2. The method defined in claim 1, wherein the lapping compound is distributed between the seating surfaces under an injecting pressure in opposition to the fluid pressure within the valve body.

3. The method of lapping the seating surfaces of valves which comprises applying uniformly distributed fluid pressure to the valve body internally thereof of a magnitude at least equal to the rated maximum working pressure of the valve, moving the valve closure member on its seat and concurrently uniformly distributing an abrasive lapping compound under sustained counter-pressure over the entire area of the seating surfaces of the valve member and body.

4. The method of lapping the seating surfaces of valves which comprises first, assembling the valve closure member on its seat in the valve body, then heating the valve member and the body to approximately the working temperature of the valve, and then introducing under pressure an abrasive lapping compound over the entire area of the seating surfaces while relatively moving said closure member and valve body to eliminate mechanical distortions thereof incident to assembly and heating of the valve parts.

5. The method of lapping the seating surfaces of valves which comprises simultaneously heating and subjecting the valve body and closure member to pressure, at least equal to the rated 10 working temperature and pressure of the valve, by retaining a heated fluid medium under uniformly distributed pressure within the valve body. and uniformly distributing an abrasive lapping compound under sustained counterpressure between the seating surfaces of the valve member and body, while one of said surfaces is moved in parallelism with the other.

6. The method defined in claim 5, in which said fluid medium is an inert, non-combustible gas substantially neutral to the abrasive compound. I

'7. The method of lapping a lubricated valve having a body and closure member with lubricant distributing grooves in. one of said valve parts, which comprises first assembling the closure member on its seat, then supplying a fluid pressure medium within the valve body to subject the valve parts to a uniform internal pressure at least equal to the maximum rated working pressure of the valve, and then introducing an abrasive lapping compound between the seating surfaces of said closure member and valve body through said lubricant distributing grooves, while simultaneously oscillating said closure member on its seat.

8. The method of lapping lubricated plug type valves in which the valve plug is provided with peripheral lubricant distributing grooves, which comprises first assembling the plug in seated position in the valve body and yieldingly urging the plug to its seat, retaining a fluid medium within the valve body under a predetermined pressure at least equal to the rated maximum working pressure, and then injecting an abrasive compound under counterpressure, through said lubricant distributing grooves, between the seat- A ing surfaces of said plug and valve body, while simultaneously oscillating said plug on its seat.

9. The method of lapping the seating surfaces of plug-type valves which comprises first assembling the valve plug on its seat and applying a predetermined yielding pressure resistance to axial movement of the plug out of contact with said seat, then confining within the valve body a non-oxidizing gas under pressure at least equal to the service line pressure for which the valve is designed, and then uniformly distributing an abrasive compound under counter-pressure over the entire area of the seating surfaces of the valve plug and body while simultaneously relatively moving said surfaces about the axis of the valve plug.

10. The method of lapping the seating surfaces of plug-type valves, which comprises first assembling the valve plug on its seat in the valve body, then confining within the valve body a fiuid medium at a temperature and pressure substantially corresponding to the ultimate working temperature and pressure of the valve, and then relatively moving the seating surfaces of said valve body' and plug while maintaining a substantially continuous fiow of abrasive compound between and in contact with said surfaces.

11. The method defined in claim 10, wherein a regulated counter-pressure is applied to tli e abrasive compound in proportionate ratio to the temperature and pressure of said fluid medium.

12. The method defined in claim 10, wherein said fiuicl medium is a non-oxidizing gas substantially neutral to the abrasive compound.

13. Apparatus for lapping valves comprising in combination with an assembled valve body and valve member, conduits connected with opposite ends of the fluid line passage through the valve body and member while relatively moving said surfaces in parallelism with each other.

14. In apparatus for lapping valves having a valve body and a rotatable valve plug seated within said body, means for applying variable axial pressure to the plug to yieldingly urge the a same to seated position, an operating stem for said plughaving an axial bore, a lubricant receiving chamber surrounding said stem, means for confining a fluid medium within the valve body at a pressure and temperature approximating the working pressure and temperature of 15 Number the valve, means for maintaining lubricant pressure in. said chamber exceeding the fluid pressure in the valve body, and means for injecting an abrasive lapping compound through said bore 'of the operating stem and uniformly distributing the same between the seating surfaces of the valve plug and body. e

GEORGE F. SCHERER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I'ENTS I Name Date Eynon Mar. 31, 1914 Weber Aug. 28, 1928 Scherer Jan. 6, 1942 

